Echad hamarbeh ve’echad hamam’it ubilvad sheyichavein libo lashomayim.
Clearly chamira sakanta meissura, and there is clearly no heter to drink so much that you can’t daven or bentch. The mishna brurah is clear on this point, and I have yet to see someone who argues and holds that these mitzvos do not apply on Purim. Bentching is a deoraysa, and so is Krias Shma. Even on Purim, they’re halachos deoraysah, not chumros.
The famous bochur who almost died from alcohol poisoning on Purim should give us all pause. The Maharsh”a in Maseches Megillah says “shachtei Raba lereb Zeira” meant that he convinced him to drink too much and Reb Zeira became mortally ill. The Maharsha also adds in bava metzia that a tzurva merabbanan is allowed to claim on Purim that “lo yada” even tho he’s in a state of “yada”.
Finally, the Gr”a and many others say that “ad delo yada” means an inability to calculate the gematria of “arur Haman” and “baruch Mordechai”.